Background: Potassium replacement protocols are commonly used in ICUs to standardise replacement and minimise harm. Yet, there is variability in potassium replacement practices.

Aims: (i) To examine relationships between potassium levels, potassium administration, and the potassium replacement protocol; and (ii) to explore factors influencing potassium replacement decision-making.

Methods: An exploratory mixed methods approach using retrospective audit and interviews was undertaken. Clinical data from two ICUs were extracted about potassium results, potassium administration and other related data from the first 72 h of ICU admission, for all patients admitted between January 2015 and December 2022. Critical care nurses were interviewed between January and March 2024, with interviews professionally transcribed and analysed using inductive content analysis.

Results: From the sample of N = 10,613 patients, n = 132,507 potassium results were analysed. Potassium replacement was indicated for 39.7 % (n = 52,592) of potassium results. When replacement was indicated, potassium was administered within 2 h in 59.9 % (n = 31,508) of cases. Interviews with critical care nurses (n = 21) lasted 5-28 min (mean 12 min). Interview participants indicated that potassium replacement decisions were influenced by the patient's history and current condition, and colleague consultation. There was little concern over potential risks associated with potassium replacement. Greater clarity around the purpose and compulsoriness of potassium replacement protocols was desired.

Conclusion: These findings offer valuable insights into the intricacies of protocolised potassium replacement adherence and deviations across two ICU settings. Autonomy and interprofessional collaboration emerged as a key factor, with nurses exercising decision-making ability underpinned by patient specific considerations, assessment, and clinical judgement.

Implications for clinical practice: When protocols are used to guide potassium replacement and other electrolytes, clear guidance as to the compulsoriness of the protocol is needed. Alternately, with safety a priority, when and how clinicians may use their clinical judgement and discretion in potassium replacement must also be explicit.

Keywords: Clinical decision-making; Clinical protocols; Critical Care; Hypokalaemia; Intensive Care; Nurses; Patient safety; Potassium replacement; Protocol.

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